Current polymeric dental restorative composite precursors have remained largely unchanged for the last 25 years. These materials have several short- comings including (a) the need for large amounts of filler for mechanical strength, (b) incomplete curing, (c) shrinkage, and (d) long term degradation of adhesion. In order to overcome these limitations, advances must be pursued in totally new candidate materials. We propose the use of silsesquioxane hybrid monomers of the formula [(SiO1.5)8(OR)x(OSi[CH3]2R')8-x], where R is a short alkyl chain and R', a polymerizable group such as epoxy rings or ring-bound alkenes. These materials feature the combination of a rigid (SiO1 .5)8 core (imparting strength and stability) with two separate reactive groups: the -OR, which is hydrolytically sensitive and reacts with water molecules bound to the surface of the dentin, and R', for strong bulk polymerization. Other benefits include ease of processability, reduced reliance on inorganic fillers, and increased resistance to an oral environment. Our Phase I objectives to demonstrate the potential of these materials are (1) the synthesis and characterization of relevant silsesquioxane monomers; (2) the determination of their curing behavior; (3) evaluation of their mechanical properties; (4) study the compatibility with nanophase oxides (i.e., TiO2, ZrO2) for cosmetic effects; and (5) preliminary model studies on their durability in oral environments. In Phase II we will further improve the performance of these materials by iterative structure/property studies and proceed with more rigorous studies on their behavior under clinical conditions. PROPOSED COMMERCIAL APPLICATIONS: In addition to the intended function as dental restoratives, these materials could have applications in other medical prosthetics, matrix materials for fiber matrix composites, and advanced adhesives.